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PM connecting Rods

I was just browsing the threads at the diesel stop and I hear people talk about PM (Powdered Metal) rods!!! I thought all 7.3 and 6.9 had forged rods? They say even the new 6.0 even has PM rods? Is this true, god I feel betrayed!

All 6.0 have PMR. but it is a different rod design compared to the 7.3, and it is stronger. 7.3's made after Oct. 15 , 2000 have PMR. The 7.3's had some engines that were made after that date that still had forged rods cuz the PMR supplier couldn't keep up with the engine assembly line production demands. 7.3 PMR engines in stock form will last a long time. If you mod a PMR 7.3 it depends on what mods and application as to how long it will last.

The powdered metal is made by spraying molten metal in a fine mist, the particles solidify quickly and a powder is formed. The metal powder is coated with a binder. After this, the powder is then placed in a die and compacted. This "green" part is then heated to the austenitic (just before complete melting) range of the steel so the particles in the part "fuse" together this is called sintering. However the flaw to this process over conventional press forging is that the parts are not 100% dense. Usually PM parts are 70-90% (100% is not really necessary if it was, conventional forging would be used) the density of cast steel, while press or drop forged pieces are typically 125% - 150% the density of a poured steel. This equates to a lighter (more airy if you will) part when using the PM process. The main use for PM parts is self lubrication. By making a part say 30% oil or graphite and 70% steel you have self lubricated parts.

When forging conventional solid connecting rods you must cut the bearing caps off the "big end" of the rod after rough forging. Then the mating surfaces are milled flat, the pieces are bolted together and then the "big end" hole is bored to spec.

All of these processes are eliminated in PM rod forging. When using powdered metal, the rough shape of the rod is determined during compaction, then the "big end" rod cap is pulled off (this "green" compacted part is very week before sintering) then the part is heated and sintered and your done. Thus eliminating the need for cutting and milling the mating surfaces, and then boring the bearing hole to specs (these are costly operations requiring CNC machine operation). Also the overall advantage to PM parts is they are very dimensionally accurate without machining (I believe tolerances today are +-0.001"). Just thought I add that for ya if no one already knew. Sure the PM parts may be more rigid but the strength just cant be the same so are they really superior?

Yes, but due to the inherent nature of a PM part they are only 70% - 90% the density of a cast steel while say a conventional press forged part is 125% - 150% the density of a cast steel. Meaning they are not as strong. The obvious advantage to the "cracked cap" rods are, they eliminate the machining processes needed after conventional forging. These are milling the mating surfaces, bolting the cap and rod together and then boring the bearing hole (time consuming operations requiring setup and teardown on a CNC machine). The cracked cap PM rods require little to no machining (I think tolerances for PM parts these days are +-.001"?). So I guess like everything else these days quality has succumb to efficiency eh?